The invention concerns an electrical machine, specifically a rectifier-energized synchronous machine with permanent magnet excitation. A machine of this category is known from the unpublished German Patent Disclosure No. 37 05 089.3.
The peculiarity of this design is constituted by the fact that the rotor comprises essentially a central disk to which, in the area of the outer circumference and on both sides, a ring-shaped pole body structure that is coaxial with the rotor shaft is attached. This pole body structure consists of a defined sequence of permanent magnets and soft iron components which alternately are arranged side by side and in peripheral direction.
The permanent magnets and soft iron components are jointly embedded in plastic, true to measure and in ring-shaped fashion, and as well fastened on the central disk in axial direction. The central disk itself consists preferably of fiber-reinforced plastic. The free end of each pole body structure, away from the disk, features a cover plate which consists as well of plastic.
Arranged around the inner and outer circumference of the pole body structure are pole elements which are integral parts of the stator of the machine and feature inside coils through which flows current. Directed toward the pole body structure of the rotor are open pole shoes which, except for a slight air gap, extend up to the rotor.
The magnetic flux properties demand that the rotor, in its supporting mechanical components, be made extensively from plastic. The pole body is thus given an inhomogeneous structure where, for one, the metallic permanent magnets and soft iron components are embedded with their mass in plastic which, on the other hand, however, has a modulus of elasticity that is about ten times as low as that of steel. Consequently, the rotor is a labile component which operationally tends to any type of vibrations, specifically flexural vibrations. This, in turn, leads to unequal air gaps between the pole bodies and pole shoes. Unfavorable in this context are not only air gap differences between the right hand and left hand side but specifically between the air gaps on the inner and outer circumference of the pole bodies. The result is a disturbed flux line pattern during rotation, which expresses itself in a considerable noise generation and poor efficiency. Therefore, machines of this type cannot be manufactured yet for higher output and/or speed of rotation.
The problem underlying the invention is to so design an electrical machine according to the categorial definition that the run performance of the rotor will be improved and the capacity of the machine can be increased.